What is microchimerism and how does it affect the mother’s health?

° Сchimeras—fantasy creatures composed of various animal parts—have appeared in various cultures, representing the wondrous, the grotesque, and the inherent complexity of identity. In ancient Greece, the chimera was part lion, part goat, part snake. In classical Japanese history, he is composed of a monkey, a tiger and a dog. Modern biology now claims that humans can also be chimeras, containing cells of different genetic origin.

Christine Chua, a postdoctoral researcher in biology at UC Santa Barbra, studies one form of chimerism — microchimerism — that occurs when cells are exchanged between mother and fetus during pregnancy. Her work has the potential to help reinvent the way scientists define the human body, as well as open new avenues for understanding and improving maternal health.

As part of a group of researchers developing more sophisticated tools to study microchimerism, Chua is also advancing the practice of biological anthropology, a science that grapples with diversity and ethical approaches to the study of humans.

“[Microchimerism] it’s still such a small field that there are challenges in terms of workflows, data collection and recruitment,” said Chua, who was recently named one of STAT’s 2023 Wunderkinds. On the other hand, she said, “it’s very exciting because there’s an opportunity to ask questions that we haven’t been answered, or to open up spaces for other people to develop our thinking.”

For decades, scientists suspected that cells from developing offspring could escape the uterus and travel through the bloodstream into the mothers’ bodies, eventually settling in the brain, heart, lungs and other organs. However, researchers have only recently begun to explore how these fetal cells may affect the mother’s health, from potential benefits—faster wound healing and greater resistance to cancer—to disadvantages, such as increased susceptibility to autoimmune diseases.

One of the difficulties of this nascent science is the rarity of fetal cells in mothers’ bodies, which range from 1 in 100,000 during pregnancy before dropping to just 1 in a million after birth.

According to Sing Sing Way, a professor and researcher at Cincinnati Children’s Medical Center, the lack of tools and laboratories studying microchimerism has kept the field from getting the recognition it deserves. “It’s fundamental to how we determine which cells are in our body,” he said. “In high school we are taught that all the cells in our body are coded by our DNA… and [having exceptions to that] would fundamentally change the way our bodies work.

hHistorically, scientists have studied microchimerism in mothers with sons, using the Y sex chromosome, which is only present in males, to distinguish between maternal and fetal cells. In a 2015 study, for example, pathologists examining the bodies of 26 women who died during or shortly after pregnancy found cells with Y chromosomes in every organ examined, including hearts, brains and kidneys.

Chua, who is a key part of an international research team – known as the Microchimerism, Human Health, and Evolution Project – used more precise genetic markers capable of detecting differences in genes related to the immune system that vary widely between mothers and fetuses of both skirt.

In collaboration with local hospitals and mothers-to-be donating blood samples, Chua is investigating how microchimerism varies in pregnant people, and how this variation may affect the health of the mother and baby. One hypothesis is that the mother’s immune system, which can be triggered by and in turn attack fetal cells, plays a role in determining the amount of microchimerism in the parent. Going a step further, Chua also plans to study the role of stress and sociocultural factors that can modulate immune activity and thereby alter the balance of maternal and fetal cells in the mother’s body.

“Kristin takes on a project that’s quite complex and even adds another really important layer by putting it in the context of social human work,” said Amy Boddy, an associate professor of anthropology at the University of California, Santa Barbara, who leads the lab Chua runs in.

According to Boddy, taking into account how sociocultural circumstances influence biology is crucial because humans are social animals. This type of effect cannot be seen in a petri dish or database, and is an important component of research that is now gaining attention.

“You don’t find many people out there who can really speak to both sides when it comes to biology and the cultural determinants of certain factors,” Boddy said. “Christine is right at the top of the field because she has experience in both. “

Christine Chua (far right) gives a lecture at one of her partner universities in the Philippines. Courtesy of Christine Chua

° Сhua began to navigate cultural and social dynamics long before he became a scholar. A second generation Chinese Filipino American, she was raised in Los Angeles and nearby Rancho Cucamonga. In elementary school, Chua’s teachers asked her parents to stop speaking Filipino at home so that she would learn English faster.

“It was good at the time,” she said, “but since there was no Filipino spoken in the household and only English was spoken, the language was lost.”

With her mixed heritage, Chua recalls sometimes feeling culturally outcast among friends who would argue that her way of doing things was not properly Filipino or Chinese. “I don’t know if it was an identity crisis,” Chua said, “but I would think, ‘Huh, that’s really weird.'”

When Chua began studying anthropology at the University of California, Los Angeles, the field grappled with questions of identity and power dynamics that resonated with her personal experience. In particular, anthropologists recognize the ethical complexities of extracting data from communities that are often less affluent and more vulnerable than the Western countries where most research originates.

“I’m not saying that only people who are part of that community should do it [anthropological] research because then we won’t do anything,” Chua said. “But it’s more important to acknowledge your background, your position, where you’re coming from and how that might affect the questions you ask and some of the interpretations.”

For Chua, who launched a pilot study in 2018 in the Philippines on how the stress of an authoritarian political regime can be transmitted from pregnant women to their unborn children, it meant rethinking her relationship to being Filipina, as well as considering how best to contact local hospital staff and study participants.

A key step in this process was relearning the language and cultural norms and engaging the research participants on a personal level. For example, while collecting hair samples to measure long-term cortisol levels during pregnancy, Chua found that some women who believed that cutting their hair during pregnancy would cause their remaining hair to fall out were reluctant to donate samples. The finding “was important to consider when designing future studies that require hair samples,” she said.

Chua also contacted a woman who was in labor for four days and kept returning to the hospital. “On the second or third day, we were already friends,” Chua said. “She’ll ask me where I’m from and compare and contrast the cultural differences between the United States and the Philippines.”

Chua’s fieldwork changed the way she viewed her multicultural heritage. “Growing up, it wasn’t cool to be Asian … so I tried really hard to be more American,” she said. “But it was important for me to realize that there’s a lot more to me than just being an American.”

° СHua hopes this kind of approach will inform new standards in science.

“In terms of biological anthropology, traditionally there hasn’t been much community engagement,” said Chua, who co-founded the DEI group as an undergraduate at UCLA. “But now there’s pressure to have better ethical practices, to do more than just drop by, learn, leave and never come back to the community we’re working with.”

For Chua, community engagement included advising her Filipino researchers on how to set up new lab equipment for their own studies, as well as working with expectant mothers to improve maternal mental health studies.

Talking to pregnant women in the Philippines about their experiences “made me think a lot about how there’s no universal definition of stress” and the complexity of approaching mental health issues in populations that don’t really talk about it, Chua said. Addressing mental health disparities in the U.S., she explained, may require using a different language that helps people of different backgrounds better express what they’re feeling. “I think we should be asking about mental health, but the way they’re asking in hospitals and in the U.S. medical system, they’re probably not asking in a way that makes people feel comfortable talking about it.”

According to Abigail Bigham, Chua’s advisor and associate professor of anthropology at UCLA, listening to communities and helping them articulate their needs and research interests is a critical component of human research. “Kristin is the perfect example of someone who thinks about the lives of the communities she works with and how she can contribute to the ways in which they conceptualize how they would like their well-being to improve.”

In Bigham’s experience, anthropologists and biologists are slowly changing their attitudes toward the study of humans. Rather than viewing people as passive objects of research, researchers see them as active participants who can help shape the project and contribute key insights.

It’s an approach that Chua continues to refine in her current microchimerism research and plans to incorporate into future studies. “We’re not there yet. We’re still at this point where we’re trying to make changes,” Chua said, “But it’s starting and it’s really exciting.”

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